To inject a service into an Angular component, you use the @Injectable() decorator. This decorator is applied to the service class, allowing Angular's dependency injection system to recognize and provide the service when requested by a component. The other options (@Component(), @Service(), @InjectService()) are not used for this purpose.

When using the OnPush change detection strategy in Angular, a component will be checked if a new object reference is passed to one of its inputs. This means that the component will only re-render if there's a change in the input values. The OnPush strategy is an optimization to reduce unnecessary checks and re-renders.

Change detection in Angular can be optimized by ensuring data structures are immutable. Immutable data structures ensure that when changes are made to data, a new reference is created, which helps Angular's change detection mechanism identify changes efficiently. By contrast, mutable data structures may not trigger change detection as expected.

When Angular uses the ViewEncapsulation mode "Emulated," it adds unique CSS classes to styles to achieve scoped styling. This means that styles defined in one component won't affect styles in other components, ensuring encapsulation and preventing unintended CSS conflicts. The unique CSS classes are generated dynamically to maintain separation between components, enhancing modularity and maintainability in Angular applications.

To intercept and modify HTTP requests globally in an Angular application, you would implement a class that uses the HttpInterceptor interface. This interface provides methods for intercepting both the request and the response, allowing you to add headers, modify requests, or handle errors at a global level.

When you want to conditionally replace a specific part of your component's view with another component dynamically, you typically use ngIf. This structural directive allows you to conditionally render or remove elements based on a given expression. ngFor is used for rendering lists, ngSwitch for conditional rendering based on a value, and ngReplace is not a standard Angular directive.

The main advantage of using Lazy Loading in Angular applications is faster initial loading. Lazy loading allows you to load specific parts of your application only when they are needed, reducing the initial bundle size and improving the loading speed.

To ensure that cart-related operations are handled by a single instance of a service, you can create a shared service for cart operations and provide it at the root level using Angular's providedIn. For product listing operations with different configurations on different pages, separate services for each page may be necessary to manage unique settings.

The methods setValidators() and clearValidators() belong to the AbstractControl class in Angular's Reactive Forms. AbstractControl is a common base class for FormControl, FormGroup, and FormArray. These methods allow developers to set and clear validation functions for form controls, providing control over input validation in reactive forms.

Angular provides a set of classes like Renderer2 to safely manipulate the DOM without direct access. These classes abstract away direct DOM manipulation, promoting a safer and more Angular-friendly way to interact with the DOM. ElementRef is used to access the underlying DOM element, not to manipulate it directly. DomManipulator and Renderer3 are not standard Angular classes.